UTRAN (UMTS Terrestrial Radio Access Network) is a collective term which includes the Radio Network Controller (RNC), the 3G radio base stations (Nodes-B) and the air interface to the User Equipment (UE). More particularly, Node-B handles radio channels, including the multiplexing/demultiplexing of user traffic (voice and data information).
Traffic scheduling is needed when a plurality of users has physical resources allocated onto a specific shared channel, as in the High-Speed Downlink Packet Access (HSDPA). Typically, the High Speed-Downlink Shared Channel (HS-DSCH) is used as transport channel by the User Equipment (UE) for receiving and by Node-B for transmitting data packets.
In the standard protocol HSDPA, scheduling strategies and packet schedulers are widely known. For HSDPA, the packet scheduler is located at the MAC-hs sub-layer of OSI layer 2 on the UTRAN side, in accordance to the technical specification 3GPP TS 25.321 “Medium Access Protocol (MAC) Specification (Release 5)”.
FIG. 1 shows the MAC-hs model specified by 3GPP TS 25.321 v5.13.0 for traffic handling in a 3G base station (Node-B). The MAC-d flows (1) consist of traffic on a transport channel dedicated to a specific UE, containing packets with one or several priorities. These packets are buffered by the MAC-hs entity (2) in the Node-B using a priority queue distribution entity (3). There exists a scheduling/priority handling routine that select which priority queue (4) can transmit the traffic, belonging to a user or multiple users, at a certain transmission time interval —TTI-; in HSDPA, the typical value of TTI is 2 milliseconds. Various selections can be done at every 2 ms i.e., every TTI or scheduling instant, generally speaking The selected priority queue (4) has resources allocated for transmission by a Hybrid Automatic repeat Request—HARQ- entity (5), which supports one or more HARQ process per HS-DSCH per TTI for storage of the scheduled packet to be transmitted or retransmitted. A Transport Format and Resource Combination —TFRC- selection routine (6) determines how much physical resources must be allocated for each packet to be transmitted on HS-DSCH (7). MAC control processes (8) and associated signalling in uplink and downlink (9, 9′) are also involved for exchanging information between layer 2 and physical layer.
The 3G specifications provide traffic with different Quality of Service (QoS). The attributes of QoS are mapped onto the transport format and the priority parameters of the transport channels. A Scheduling Priority Indicator (SPI) is sent to the Node-B together with the corresponding payload within every data packet. The SPI consists of 4 bits; hence, 16 different priorities can be distinguished. Although the Node B Application Part (NBAP) standard (3GPP TS 25.433) specifies these priorities, it is vendor-specific how the different priorities are handled by the Node-B.
On the other hand, the UE feeds back a channel quality indicator (CQI) report to provide the base station scheduler with channel-state information.
Within the 3G networks, the HSDPA uses a scheduler in the Node-B that has to be optimised to differentiate traffic/users to provide the appropriate Quality of Service to everyone. Most of the algorithms for HSDPA scheduler are based on throughput measurements. Several HSDPA scheduling strategies are also based on delay but with complicated functions which are difficult to implement in the infrastructures of the current 3G networks. The algorithm used in the current HSDPA networks is the weighted proportional fair, wherein the scheduling priority (SchedP) of a user is calculated by equation 1:
                    SchedP        =                                            R              ⁡                              (                t                )                                                    r              ⁡                              (                t                )                                              *          SPIweight                                    (                  equation          ⁢                                          ⁢          1                )            
In equation 1, R(t) is the instant rate of the UE that can be reached according to the reported CQI at the scheduling time t, r(t) is the user scheduling rate in the last T seconds and SPIweight is the weight of the user taking into account its priority. The user scheduling rate r(t) is representing the throughput in the Node-B.
Normally, the SPIweight is a relative weight between different users, therefore a determined fix value is given to every SPI parameter (there are a maximum of 16 different SPI values) and these 16 possible SPIweight values are defined in the 3GPP standards.
The HSDPA scheduler calculates the different scheduling priorities (SchedP) of the packets every tti, i.e., every 2 ms, taking into account the different inputs, and then the HSDPA channel is allocated to the packet with the highest scheduling priority (SchedP). This scheduling priority (SchedP) is a fixed value, independent from the packet delay. If the HSDPA dedicated transport channel allows more than one packet per tti, then the next packet to be transmitted is chosen from the packets with a higher priority value buffered in the corresponding priority queue.
However, there are several kinds of applications/users that need different QoS priorities, not only in terms of throughput but also in terms of delay. Furthermore, simplification of algorithms is desirable. Therefore, the HSDPA scheduling optimization requires for considering the packet delays in the calculation of the scheduling priorities as well as simplifying said calculation.